1. Field of the Invention
The present invention relates to a valve timing adjusting device that adjusts valve timing of an actuated valve, which is opened and closed by a camshaft using torque transmitted from a crankshaft, in an internal combustion engine.
2. Description of Related Art
Conventionally, there has been known a valve timing adjusting device adjusting a relative phase (engine phase) between a crankshaft and a camshaft, which decides valve timing, according to brake torque generated by an actuator. As a kind of such the valve timing adjusting device, Patent document 1 (JP-A-2008-51093) describes a device that adjusts an engine phase by generating brake torque using an actuator.
More specifically, the actuator described in Patent document 1 passes a magnetic flux through a magnetic viscous fluid that is sealed in a fluid chamber inside a housing and that contacts a brake rotor, thereby variably controlling viscosity of the magnetic viscous fluid. With such the actuator, brake torque corresponding to the viscosity of the magnetic viscous fluid is inputted to the brake rotor that rotates in a constant direction. Therefore, a phase adjusting mechanism linked with the brake rotor adjusts the engine phase in accordance with the brake torque.
Specifically in the actuator of Patent document 1, the brake rotor is penetrated through the housing between an inside and an outside of the housing in order to link the brake rotor inside the housing with the phase adjusting mechanism outside the housing. Therefore, in order to inhibit a situation where the magnetic viscous fluid leaks from the fluid chamber inside the housing to the outside of the housing and changes input characteristics of the brake torque, a sealing structure using an oil seal or magnetic poles is provided between the housing and the brake rotor. If the change in the input characteristics of the brake torque is suppressed, fluctuation in adjustment characteristics of the engine phase, which follow the brake torque, becomes less apt to occur. Therefore, reliability can be secured.
In order to suppress the leakage of the magnetic viscous fluid by exerting the sealing action in the sealing structure using the oil seal in the actuator of Patent document 1, it is necessary to strengthen tension of the oil seal applied to the brake rotor. However, if the tension is strengthened, wear can be caused in the oil seal by friction resistance, thereby deteriorating durability.
In the case of the sealing structure using the magnetic poles in the actuator of Patent document 1, it is essential to provide a certain clearance to allow rotation of the brake rotor between a magnetized portion of the brake rotor forming the magnetic poles and a bearing of the housing. Therefore, there is a possibility that the leakage of the magnetic viscous fluid to the outside of the housing through the clearance between the magnetized portion and the bearing cannot be suppressed sufficiently, thereby causing a bottleneck against improvement of sealing performance.